let able = true;
window.onscroll = function () {
    if (able) {
        RecentCourse();
        able = false;
    } else {
    }
}

function RecentCourse() {
    let timer = setInterval(Shadow, 200);
    let blur = 0;
    let spread = 0;
    function Shadow() {
        let courses = document.getElementsByClassName("courses");
        if (blur < 11) {
            blur = blur + 2.2;
        } else {
            clearInterval(timer);
        }
        if (spread < 5) {
            spread++;
        }
        courses[0].style.boxShadow = "0 0" + " " + blur + "px" + " " + spread + "px" + " " + "rgba(128, 128, 128, 0.21)";
    }
}